Organic compounds containing acrylic groups are well known to require protection from heat during their processing, storage and use as reaction intermediates. Such protection is generally afforded by the addition of a small quantity of a stabilizing compound to the organic compound. Thus, for example, in U.S. Pat. No. 4,021,310 to Shimizu et al., a method for inhibiting the polymerization of acrylic acid or acrylic esters during distillation is disclosed. Here, the distillation is carried out in the presence of (A) at least one compound selected from hydroquinone, hydroquinone monomethyl ether, cresols, phenols, t-butyl catechol, diphenylamine, phenothiazines and methylene blue; (B) at least one compound selected from copper dimethyldithiocarbamate, copper diethyldithiocarbamate, copper dibutyldithiocarbamate and copper salicylate; and (C) molecular oxygen. This patent does not suggest that this method is applicable to the stabilization of any silicon compound, much less an acryl-functional halosilane.
It is also known that acryl-functional halosilanes are particularly susceptible to thermal polymerization during their preparation and subsequent purification by distillation. Furthermore, safety considerations often dictate that oxygen levels be kept low during the preparation and distillation of acryl-functional halosilanes in view of the potential of fire or explosion. With this observation in mind, some compounds which do not require the presence of oxygen in order to act as stabilizers for the acryl-functional halosilanes, such as phenothiazine, have been employed in the art. This is exemplified by U.S. Pat. No. 4,558,111. In this patent, Tolentino discloses a method for making acrylate-functional halosilanes or halosiloxane by reacting an organic acrylate and a halosilane or halosiloxane having at least one silicon-bonded hydrogen atom. The reaction takes place in the presence of a hydrosilation catalyst and an amount of inhibitor effective for preventing the thermal free radical polymerization of the organic acrylate. This disclosure mentions at least seven inhibitors and illustrates the preparation of different chlorosilanes using phenothiazine as the inhibitor while purging the reaction flask with nitrogen.